1. Field of the Invention
The present invention relates to a semiconductor device and to a method of fabricating the same. In particular, the present invention relates to a semiconductor device having a package structure of a BGA or a CSP type and to a method of fabricating such a semiconductor device.
2. Description of the Related Art
In recent years, with the increasing demand for small, light and thin electronic apparatuses, smaller, lighter, and thinner semiconductor devices are required. In order to satisfy this demand, semiconductor devices having package structures of the BGA and the CSP types have been developed.
A semiconductor device having a package structure of a BGA or a CSP type comprises a semiconductor chip, an FPC tape such as a TAB tape for mounting the semiconductor chip thereto and solder balls arranged on the TAB tape. The semiconductor chip is fixed to the TAB tape by a die bonding material. The TAB tape has bonding pads and ball pads, the bonding pads and the ball pads being interconnected in the TAB tape by a wiring pattern. The semiconductor chip is connected to the bonding pads of the TAB tape by wires.
The solder balls are arranged on the ball pads of the TAB tape and thus function as external electrodes. As a result, the semiconductor chip and the solder balls are electrically connected to each other by the TAB tape as an interposer. In the case where a semiconductor device of surface mount type having solder balls functioning as external terminals, such as a semiconductor device of BGA or CSP type, is mounted to a motherboard, the semiconductor device is, in general, heated in a solder reflowing equipment having an ambient temperature of about 250.degree. C. to connect the melted solder balls to the electrode pads of the motherboard.
Also, it is conceivable to attach a buffer resin sheet to the TAB tape to reduce the stress arising due to the difference in the coefficient of thermal expansion between the semiconductor chip and the TAB tape, and to apply the die bonding material to the buffer resin sheet to thereby fix the semiconductor chip to the TAB tape.
In the semiconductor device in which the semiconductor chip is fixed on to the TAB tape by the die bonding material and sealed by the sealing resin, moisture is contained in the polyimide constituting the TAB tape, the sealing resin and the die bonding material. Especially, the polyimide making up the TAB tape is a material which easily absorbs moisture. Therefore, when the solder balls are reflowed to mount the semiconductor device to the motherboard, the moisture contained in the TAB tape, the sealing resin and the die bonding material is evaporated with the increase in temperature and the vapor causes cracking and/or bulging of the semiconductor device.
In order to solve this problem, a method has been proposed in which small holes are formed through the TAB tape before the semiconductor chip is mounted to the TAB tape, so that the moisture contained in the semiconductor device may be released through the small holes when the solder balls are reflowed after the semiconductor chip is mounted to the TAB tape. The cracking and bulging of the semiconductor device can be prevented by releasing the moisture contained in the semiconductor device.
However, if small holes are formed in the TAB tape in advance, the die bonding material between the semiconductor chip and the TAB tape may flow and may fill up the holes of the TAB tape at the time of heat treatment during the fabrication process of the semiconductor device, with the probable result that the holes fail to function as vapor escape holes. It is also possible that the die bonding material flows through holes of the TAB tape and contaminates the reverse side of the TAB tape or the jigs or tools to be used. In the case where the buffer resin sheet is attached to the TAB tape, on the other hand, the buffer resin sheet blocks the flow of the die bonding material, but the buffer resin sheet is melted and fills up the holes of the TAB tape, often leading to the failure of the holes to function as vapor escaping holes.